Lithofacies and Sandstone Petrofacies of Permo-Carboniferous Gondwanan Sediments from Northwestern Bangladesh and Jharia Coalfield of India
Nur Uddin Md. Khaled Chowdhury
Auburn University, Department of Geology and Geography, Auburn, Alabama, USA
The Permo-Carboniferous Gondwanan sequences are well-distributed in the Indian subcontinent, South Africa, Madagascar, Australia, Antarctica, and South America bearing proof that the southern continents were once united in the form of Gondwanaland. These sequences in the Indian subcontinent were initially deposited in one master basin which got segmented during Gondwanan rifting due to extensional tectonics. Lithofacies and petrofacies assemblages were studied from several drilled cores of northwestern Bangladesh and outcrop sections in the Jharia basin of India to document systematic changes that can be linked to major shifts in sources and depositional environments.
The five distinct lithofacies identified based on rock types, colors, sedimentary structures, and bedding styles are sandstone, coal, mudstone, black shale, and conglomerate lithofacies. The sandstone lithofacies which is further divided into sub-lithofacies is composed of fine to coarse grained, gray to greenish, massive to bedded sandstone. The coal lithofacies is characterized by black to dark gray, laminated coal. The mudstone lithofacies which is again subdivided into two sublithofacies refers to massive to laminated clays with spars of silt and sand. The black shale lithofacies is characterized by black, fine grained, laminated clay with tiny silt sized particles. The conglomerate lithofacies consists of matrix supported, brecciated pebbles within medium to coarse grained sand.
Based on modal analysis three compositionally distinct petrofacies (quartzose, quartzolithic, and quartzofeldspathic) have been identified. This ongoing study suggests sudden and gradual shift in provenance from stable craton to orogenic systems along with various fluvial regimes in deposition environment.
AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects